Disposable absorbent diapers are widely used by infants and incontinent individuals. In order to provide a disposable absorbent diaper which can fit a range of wearers and minimize leaks, disposable absorbent diapers often include stretch laminates. Because the wearers of disposable absorbent diapers vary in size, conventional stretch laminates are often used in the waist region and leg regions of the disposable absorbent diaper, thereby allowing the disposable absorbent diaper to fit a wide range of wearers.
A conventional stretch laminate often has at least two nonwoven materials and at least one elastic film sandwiched between the two nonwoven materials. In general, the two nonwoven materials are attached to the elastic film via an adhesive.
Conventional stretch laminates are generally elastically extensible and can be made so by meshing the conventional stretch laminate between sets of teeth. The process can involve meshing the conventional stretch laminate between activation rolls which have protruding teeth. Typically, an activation region of the conventional stretch laminate is located between the teeth while a tack down region is not significantly located between the teeth. Because the conventional stretch laminate is intermeshed between the teeth of the activation rolls, the nonwoven materials are permanently elongated at least to a certain degree, so that upon release of the applied tensile forces, the conventional stretch laminate generally will not fully return to its original undistorted configuration. Such orientation and alignment is common throughout the industry.
This process of making a stretch laminate elastically extensible is called “mechanical activation” or “ring rolling”. The mechanical activation process is typically performed at high speeds. Consequently, the stretch laminate experiencing the mechanical activation process can be exposed to very high strain rates. Moreover, in order to provide the stretch laminate with greater extensibility, the stretch laminate may further be exposed to high percentages of strain.
Unfortunately, many stretch laminates incur defects as a result of the high strain rates and high percentages of strain experienced during the mechanical activation process. Many of the defects are structural in nature. For example, a nonwoven which experiences the mechanical activation process may incur defects such as holes which reduce the structural integrity of the nonwoven. Similarly, an elastic film which undergoes the mechanical activation process may also experience defects such as holes which also reduce the structural integrity of the elastic film.
It has been found that the amount of adhesive applied to a stretch laminate in an activation region, prior to mechanical activation, can influence the number of defects which the stretch laminate will incur as a result of the mechanical activation process. For example, too much adhesive in an activation region can overly restrict the movement of a multitude of fibers which make up the nonwoven. This restriction by the adhesive can lead to increased localized strains in many of these fibers. Unfortunately, the increased localized strain can lead to fracture of many of the fibers, thereby causing premature failure of the nonwoven.
In contrast, too little adhesive may reduce the localized strain in the fibers, thereby decreasing defects incurred by the stretch laminate during mechanical activation. However, because of reduced bonded area, too little adhesive can also reduce the peel force and reduce the creep resistance of the stretch laminate. Conventional wisdom teaches that less adhesive in the activation region detrimentally affects the peel force and creep resistance characteristics of the stretch laminate.
Consequently, a need for a stretch laminate which minimizes the use of adhesive while maintaining peel force values and creep resistance criteria exists. In addition, a method for making such a stretch laminates exists.